Female reproduction system has regular cyclic changes that teleological may be regarded as periodic preparations for fertilization and pregnancy. Periodic vaginal bleeding, the most conspicuous feature of the menstrual cycle, occurs with the shedding of the uterine mucosa (menstruation).

The average figure of the length of the cycle is 28 days from the start of one menstrual period to the start of the next, but it varies notoriously. The days of the cycle are identified by number, starting with the first day of menstruation.

Ovarian Cycle:

Under the ovarian capsule from the time of birth. Each primordial follicle contains an immature ovum. Several of these follicles enlarge and a cavity forms around the ovum, at the start of each cycle. Follicular fluid fells this cavity. One of the follicles in one ovary starts to grow rapidly on about the sixth day and becomes the dominant follicle. The other regress, forming arteries follicles.

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The arteries process involves apoptosis. Generally, the follicle which secretes estrogen inside it that is needed for final maturation is selected to be the dominant follicle. Distended follicle raptures at the 14th day of the cycle, and the ovum is extruded into the abdominal cavity. This process is called evolution. Fabricated ends of the uterine tubes picks up the ovum, and is transported to the uterus. And unless fertilization occurs, it passes out through the vagina.

If there is no pregnancy, the corpus luteum degenerates about 4 days, before the next menses i.e., 24th day of the cycle. It is eventually replaced by scar tissue, forming a corpus albicans. Menstrual blood contains prostaglandins, debris.

It also contains a large amount of fibrinolysin from endometrial tissue. Menstrual flow takes about 3-5 days. But it can flow as short as 1 day and as long as 8 days in normal women blood loss of more than 80 ml is normal. Bleeding is variable which usually occurs in less than 28 days from the last menstrual period.

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When a woman is sexually excited, fluid is secreted onto the vaginal walls due to release of vasoactive intestinal polypeptide (VIP). Vestibular glands secrete lubricating mucus. The upper part of the vagina is sensitive to stretch.

Tactile stimulation from labia minora and ditoris adds to the sexual excitement. These stimuli are reinforced by tactile stimuli from the breasts and, as in men, by auditory and visual stimuli, which may build up to erescendo known as orgasm. During orgasm, there are no autonomically mediated rhythmic contractions of the bulbocavernosus and ischiocavernosus muscles.

The body changes that develop in girls make puberty due to feminizing hormones. Women have narrow shoulders and broad hips, thighs that converge, and arms that diverge. The female distribution of fat in the breasts and buttocks is also seen in eastrate males and women have less body hair.

Gametogenesis:

Gametogenesis is the production of haploid sex cells (in humans, ovum and spermatozoa) that each carry one-half the genetic compliment of the parents from the germ cell line of each parent, see colored image 9.5.

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The production of ovum is known as cogenesis and the production of spermatozoa is called spermatogenesis. Both cogenesis and spermatogenesis provide a mechanism through which genetic information may be passed to offspring. The fusion of spermatozoa and ova during fertilization gives rise to a zygote with a fully restored diploid genome.

The production of male and female gametes is a highly complex and coordinated sequence of a mitotic division, two meiotic divisions, cytoplasm apportionment (divisions) and cellular differentiation. Any chronic alteration in the sequence of morphological and biochemical transformations required to produce gametes usually results in sterility for the affected parent.

In human makes, spermatogenesis carries the full genetic compliment of 46 chromosomes (22 autosomal pairs, one X and one Y sex chromosomes). The spermatogonium represents the germ cell line from which all sperm cells are derived. Sequentially, the process of spermatogenesis via mitosis produces a primary spermatocyte that is also diploid (2N) and then via meiosis, two secondary spermatocytes that are haploid (N). The haploid secondary spermatocytes carry 22 autonomies and either an X or a Y sex chromosome.

The secondary spermatocytes each undergo a second meiotic division to form a total of four haploid spermatids. Subsequently, nurtured by surrounding somatic cells, through the process of cellular differentiation the four spermatids produce 4 sperm cells capable of motility and fertilization. Although there is variation between sperm cells as to the exact nature of their genetic information.

In human females the germ cell line carries the full female genetic compliment of 22 autosomal pairs and two X chromosomes. Mitotic division yields a diploid primary acolyte. Meiotic divisions then produce one female gamete—the ovum. In humans, the first meiotic division is suspended in the diplonema stage during embryonic development.

Meiosis resumes, one ovum at a time following puberty and during the adulatory period of the menstrual cycle. Maturation proceeds with the production of haploid (N) secondary acolytes with 22 autosomal chromosomes and an X sex chromosome (the sex chromosome must be an X chromosome because normal human females carry two X chromosomes and no Y chromosomes). Also formed is a haploid polar body that IS nearly devoid of cytoplasm contents.

This is a fundamental difference between male and female Gametogenesis. In males, there is a nearly equal division of cytoplasm to the gametes, in females the cytoplasm contents are preserved for the eventual “egg” or ovum. Extraneous genetic material is removed via polar bodies.

Another meiotic division results in the production of an ootid and yet another polar body (the eventual number of polar vies associated with an ovum may equal as many as three if the first sloughed off polar body undergoes a subsequent division). Cellular differentiation of the ootid yields an ovum ready for fertilization.

There is a tremendous increase in ribosomal related component during ovum maturation so that the cellular machinery is present to handle the tremendous amount of translation and protein synthesis required in the rapid cellular divisions that follow the formation of the zygote.

Each generation of sexually-reproducing organisms is dependent upon the continuation of the germ cell line the germ line is also the vehicle of genetic transmission and alteration of the genome via mutations and recombination (i.e., evolution).

Gametogenesis process leads to the production of gametes. The development and maturation of sexcells through meiosis. Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.

Menstrual Cycle:

The menstrual cycle is the process by which a woman’s body gets ready for the chance of a pregnancy each month. The average menstrual cycle is 28 days from the start of one to the start of the next, but it can range from 21 days to 35 days. Colored image 9.6 shows menstrual cycle in a nutshell.

An egg starts to mature in one of the ovaries. Around the middle of the cycle, the egg leaves the ovary, a process called ovulation. The egg begins to travel down the fallopian tubes to the uterus. If the egg becomes fertilized by a sperm cell and attaches to the uterus, the woman becomes pregnant. If not, the uterus does not need the extra thick lining and it begins to shed. Colored image 9.7 shows transformation taking place in the menstrual cycle.

(a) The Follicular Phase:

In follicular phase, the hypothalamus in the brain signals the anterior pituitary gland to start secreting the hormones FSH (Follicle-Stimulating Hormone) and LH (Latinizing Hormone) to the ovaries. It is this FSH that will stimulate the maturation and release of a follicle from the ovary. The follicle, before it matures, would then secrete the hormone estrogen, which acts as a repairman in the uterine wall.

As the cells in the walls of our uterus start proliferating, leads to an increased thickness in our uterine linings. This thickening of the wall is a natural phenomenon to prepare our body for the possible implantation of the egg in the uterus where the fetus would grow for about 40 weeks. If, however, the egg does not get fertilized, the uterine linings would start to shed and this would give us the red bloody discharge.

(b) Ovulation Phase:

After the thickening of the uterine wall and the maturation of the follicle in the proliferative phase, we would then reach the ovulation phase. In this phase, the mature follicle ruptures open and the ripe egg is released. The hair­ like projections in the fallopian tube starts to sweep the egg to go to one direction. It is the hormone LH that will stimulate the opening of the follicle, release the ovum and other follicular fluids containing estrogen.

(c) Luteal Phase:

The ruptured follicle in the last phase would become a corpus luteum, which would continue secreting estrogen. However, as the levels of LH surge, the levels of estrogen lower.

The two functions of the corpus luteum are:

(i) To provide hormonal stimulus to the organs that are targeted

(ii) To regulate the menstrual cycle

If the ovum is not fertilized, the corpus luteum will continue to secrete the hormones progesterone and estrogen for 14 days, before it turns to corpus albicans. This corpus albicans do not get released out of the body with the onset of menstruation. It just stays there and builds up.

If the ovum is fertilized, the embryo will implant itself in the uterine wall and start secreting the hormone HCG (Human Chorionic Gonadotropin), which would signal the corpus luteum to continue secreting progesterone and estrogen and not turn into corpus albicans. At this stage, the corpus luteum is now called a fancier term— corpus luteum graviditatis, until the placenta is fully made and capable of producing progesterone.

(d) Menstrual Phase:

These are the phase when the uterine lining get sloughed off or get shed in a menstrual flow. The corpus luteum deteriorates into a corpus albicans if the ovum is not fertilized. There would be a decrease of the hormone progesterone and this would cause some blood vessels in the uterus to contract, which means that the blood supply is significantly lowered. The ischemic endometrial would then be shed and for about one week, we would have menstruation.